A 2C (3.6F) increase in temperature may be too much for many plants species to survive unless they are able to migrate to cooler areas, a team of scientists says.

Its concern follows on from a study of quiver trees, a slow-growing desert plant found in Namibia that can live for hundreds of years.

The group from the South African National Biodiversity Institute found quiver trees located in hotter northern parts of the country were struggling to survive in the drought conditions the area was experiencing.

However, the trees (Aloe dichotoma) growing further south, in cooler temperatures, were in much better condition.

We're asking sedentary organisms... to suddenly become able to move - that's a tough ask

Guy Midgley

Guy Midgley, one of the scientists involved in the study, said it offered an insight into the future impact of climate change on plant species.

"It highlights the whole problem of migration for organisms that are essentially sedentary," he told the Television Trust for the Environment's Earth Watch programme.

"We're asking sedentary organisms, which have achieved an equilibrium with the climate for thousands of years, to suddenly become able to move - that's a tough ask."

Quivers in the heat

The reason the researchers chose the quiver tree as the study's subject is because it is only found within a 2,000km (1,200 mile) range in the Southern Hemisphere, between 22 and 33 degrees of latitude.

Mr Midgley's colleague, Wendy Foden, has surveyed 54 sites and more than 6,000 trees to assess the health of the quivers.

I think now the world has really woken up and realised that climate change is real and it's happening

Wendy Foden

In the northern range, she found a disproportionate number of dead or dying trees.

The cause of death could have been the result of a fungal infection or animal damage, but because there was no obvious cause, she increasingly suspects drought and heat stress.

The drought in the region has been so severe that quiver trees are struggling to survive.

At the southern end of the growing range, the trees are thriving and hundreds of saplings are taking root.

However, the scientists say climate change models suggest temperatures in the area are set to increase by 2C (3.6F), leading to conditions similar to those currently found in the northern range.

Experiments carried out by the scientists showed that a 2C rise in temperatures caused heat stress in the trees, shutting down the plants' photosynthesis.

Without photosynthesis, the process by which plants use sunlight to convert carbon dioxide into energy, the trees effectively starve.

Wendy Foden has discovered that quiver trees have begun to migrate southwards as a result of changes to the climate.

But she voiced concern that the plants, which only germinate every 15 years, might not be able to cover the distances needed to stay within a suitable temperature range.

"If they're only reproducing every 15 years, they're going to need to go 40km (25 miles) in that time to actually keep within their range," she said.

"I think now the world has really woken up and realised that climate change is real and it's happening... we've just got to figure out what we do about it."

The Television Trust for the Environment's (TVE) Earth Report - All of a quiver - will be broadcast on BBC World between 20-21 April 2007. Please check schedules for further details